Individual pattern representations are context independent, but their collective representation is context dependent.

We studied context dependency of the representations underlying perceptual "goodness". Three experiments used a same-different task with classical Garner 5-dot patterns presented with an interstimulus interval (ISI) of 500 ms. Same patterns were allowed to be rotated or reflected versions of each other. Pattern goodness was varied according to rotation and reflection equivalence, using Garner's equivalence set size (ESS) measure. The ESS of both first and second patterns affected reaction time and accuracy. A model based on assumptions that Garner's equivalence sets constitute the generic representation of these patterns and that items within these sets are accessed serially was fitted to the data. Excellent fits were obtained, which were robust against frequency-induced bias at the level of the individual pattern, but sensitive to such bias at the level of the equivalence set. It was concluded that individual pattern representations are context independent, whereas their collective representations are context dependent. Simplicity and likelihood principles, therefore, seem to apply to different levels of a representation hierarchy.     

Developing human-nonhuman chimeras in human stem cell research: ethical issues and boundaries

The transplantation of adult human neural stem cells into prenatal non-humans offers an avenue for studying human neural cell development without direct use of human embryos. However, such experiments raise significant ethical concerns about mixing human and nonhuman materials in ways that could result in the development of human-nonhuman chimeras. This paper examines four arguments against such research, the moral taboo, species integrity, "unnaturalness," and human dignity arguments, and finds the last plausible. It argues that the transfer of human brain or retinal stem cells to nonhuman embryos would not result in the development of human-nonhuman chimeras that denigrate human dignity, provided such stem cells are dissociated. The article provides guidelines that set ethical boundaries for conducting such research that are consonant with the requirements of human dignity.     

Compatibility effects based on stimulus and response numerosity

Four choice reaction time experiments documented a stimulus-response (S-R) compatibility effect involving the numbers of stimuli and responses. In Experiment 1, the stimulus consisted of one or two tones, and the correct response was either one or two taps of a response key. Responses were much faster with a compatible S-R assignment, in which the number of taps matched the number of tones, than with an incompatible assignment in which these numbers mismatched. Experiments 2 and 3 replicated this effect, using visual stimuli and bimodal stimuli, respectively, suggesting that auditory/manual rhythmic compatibility is not essential to it. Experiment 4 showed that an analogous but smaller effect is obtained when stimuli are the digits 1 and 2. This new numerosity-based compatibility effect has general theoretical implications regarding the mechanisms responsible for compatibility effects and practical implications for interface design.     

From interpretation to segmentation

In visual perception, part segmentation of an object is considered to be guided by image-based properties, such as occurrences of deep concavities in the outer contour. However, object-based properties can also provide information regarding segmentation. In this study, outer contours and interpretations of object configurations were manipulated to examine differences between image-based and object-based segmentation in a visual search task. We found that locating a two-dimensional object configuration with deep concavities in the outer contour depends on the type of outer contour of the surrounding distractors. In addition, locating a three-dimensional object configuration was harder when it was surrounded by object-based-disconnected distractors, as compared with object-based-connected distractors, regardless of image-based connections in these distractors. We conclude that segmentation based on the outer contours of a target facilitates its localization. However, when three-dimensional information is available, segmentation strongly depends on object-based properties, rather than on image-based properties.     

Instability of hierarchical cluster analysis due to input order of the data: the PermuCLUSTER solution

Hierarchical agglomerative cluster analysis (HACA) may yield different solutions under permutations of the input order of the data. This instability is caused by ties, either in the initial proximity matrix or arising during agglomeration. The authors recommend to repeat the analysis on a large number of random permutations of the rows and columns of the proximity matrix and select a solution with the highest goodness-of-fit. This approach was implemented in an SPSS add-in, PermuCLUSTER, which can perform all HACA methods of SPSS. Analyses of 2 data sets show that (a) results are affected by input order, (b) instability in one method co-occurs with instability in other methods, and (c) some instability effects are more dramatic because they occur at higher agglomeration levels.     

APP23 mice as a model of Alzheimer's disease: an example of a transgenic approach to modeling a CNS disorder

Animal models are considered essential in research ensuing elucidation of human disease processes and subsequently, testing of potential therapeutic strategies. This is especially true for neurodegenerative disorders, in which the first steps in pathogenesis are often not accessible in human patients. Alzheimer's disease is vastly becoming a major medical and socioeconomic problem in our aging society. Valid animal models for this uniquely human condition should exhibit histopathological, biochemical, cognitive, and behavioral alterations observed in Alzheimer's disease patients. Major progress has been made since the understanding of the genetic basis of Alzheimer's disease and the development and improvement of transgenic mouse models. All present Alzheimer's disease models developed are partial but nevertheless essential in further unraveling the nature and spatial and temporal development of the complex molecular pathology underlying this condition. One of the more recent transgenic attempts to model Alzheimer's disease is the APP23 transgenic mouse. This article describes the development and assessment of this human amyloid precursor protein overexpression model. We summarize histopathological and biochemical, cognitive and behavioral observations made in heterozygous APP23 mice, thereby emphasizing the model's contribution to clarification of neurodegenerative disease mechanisms. In addition, the first therapeutic interventions in the APP23 model are included.     

Inferring the structure of latent class

Present optimization techniques in latent class analysis apply the expectation maximization algorithm or the Newton-Raphson algorithm for optimizing the parameter values of a prespecified model. These techniques can be used to find maximum likelihood estimates of the parameters, given the specified structure of the model, which is defined by the number of classes and, possibly, fixation and equality constraints. The model structure is usually chosen on theoretical grounds. A large variety of structurally different latent class models can be compared using goodness-of-fit indices of the chi-square family, Akaike’s information criterion, the Bayesian information criterion, and various other statistics. However, finding the optimal structure for a given goodness-of-fit index often requires a lengthy search in which all kinds of model structures are tested. Moreover, solutions may depend on the choice of initial values for the parameters. This article presents a new method by which one can simultaneously infer the model structure from the data and optimize the parameter values. The method consists of a genetic algorithm in which any goodness-of-fit index can be used as a fitness criterion. In a number of test cases in which data sets from the literature were used, it is shown that this method provides models that fit equally well as or better than the models suggested in the original articles.     

A blank look in reading: the effect of blank space on the identification of letters and words during reading

Two experiments investigated the effect of visual blank space on reading by varying the amount of interletter and interline blank space in prose passages. Increasing interletter blank spacing slowed the reading process overall, presumably because it disrupted the unitization of words and word identification, but it also improved the identification of the letters within words. By contrast, increasing interline blank spacing sped up the reading process overall, while also improving the identification of words and the letters within words, presumably because the extra spacing reduced the amount of visual information that was processed during reading. The latter finding supports the conclusion that information from surrounding lines of single-spaced text may interfere with reading.     

Every cloud has a silver lining: interpersonal and individual differences determinants of anger-related behaviors

Two studies examined the effect of status and liking of the anger target on anger behavior and individual differences in anger-related behavior. Participants recalled anger instances in which the anger target was of higher/equal/lower status and/or liked/ unfamiliar/disliked; subsequently, they indicated which behaviors they had displayed. In both studies, anger behaviors could be grouped into behaviors that imply approaching the target (anger-out, assertion, reconciliation) and behaviors that reflect avoidance/anger-in or social sharing. The results demonstrated that approach behaviors more likely occur toward lower status or liked targets; avoidance behaviors and social sharing more likely occur when the target is of higher status or disliked. On an individual differences level, an approach and an avoid/social sharing person class were identified. The findings suggest that anger may motivate prosocial behavior or social sharing, depending on the individual and type of relation with the target. Only few gender differences were found.     

Directed forgetting in working memory: age-related differences

This study explored the effects of ageing on working memory by means of the directed forgetting procedure designed by Reed (1970). Memory for a letter trigram was compared in conditions where it was either presented alone (single-item), or followed by a second trigram to be recalled (interference), or followed by a second trigram to be forgotten (directed forgetting). The results clearly indicated that elderly participants inhibited the no-longer-relevant information less efficiently (recall in the single-item condition - recall in the directed forgetting condition), as predicted by the model of Hasher and Zacks (1988). However, the results also demonstrated that sensitivity to interference (recall in the single-item condition - recall in the interference condition) increased in the condition in which no inhibition was directly required.